1. Preview Section 1 Change over Time
Population Changes
Preview
Section 1 Change over Time
Section 2 How Do Population Changes Happen?
Section 3 Natural Selection in Action
Concept Mapping

2. Section 1 Change over Time
Bellringer
The cockroach originated on Earth over 250 million years ago and is thriving today all over the world. A giant deer that was 2 m tall first appeared less than 1 million years ago and became extinct around 11,000 years ago. Why do you think one animal thrived and the other one perished?
Record your answer in your science journal.

3. Section 1 Change over Time
Objectives
Identify two kinds of evidence that show that organisms have changed over time.
Identify how the fossil record shows that changes in the kinds of organisms in the environment have been occurring over time.
Describe one pathway through which a modern whale could have arisen from an ancient mammal.
Explain how comparing organisms can provide evidence that they have ancestors in common.

4. Differences Between Organisms
Section 1 Change over Time
Differences Between Organisms
A characteristic that helps an organism survive and reproduce in its environment is called an adaptation.
Some adaptations are physical, such as fur or scales.
Other adaptations are behaviors that help an organism find food, protect itself, or reproduce.

5. Differences Between Organisms, continued
Section 1 Change over Time
Differences Between Organisms, continued
Individual organisms that share the same characteristics might be members of the same species.
A species is a group of organisms that can mate with one another to produce fertile offspring.
Groups of individuals of the same species living in the same place make up a population.

6. Differences Between Organisms, continued
Section 1 Change over Time
Differences Between Organisms, continued
Do Species Change over Time? Since life first appeared on Earth, many species have died out, and many new species have appeared.
Scientists observe that the inherited characteristics in populations change over time.
Scientists think that as populations change over time, new species form.

7. Evidence of Change over Time
Section 1 Change over Time
Evidence of Change over Time
Sediments laid down over time contain the remains of ancient organisms. Older layers are deeper, and contain older organisms.
Fossils The remains or imprints of once-living organisms found in the layers of rock are called fossils.
Examples of fossils vary from footprints to complete organisms.

8. Evidence of Change over Time, continued
Section 1 Change over Time
Evidence of Change over Time, continued
The Fossil Record By studying fossils, scientists have made a timeline of life that is known as the fossil record.
The fossil record organizes fossils by their estimated ages and physical similarities.
Comparing organisms in the fossil record can reveal how organisms have changed over time.

9. Section 1 Change over Time
Evidence of Ancestry
Scientists observe common characteristics in all life, which suggests that all living species descended from common ancestors.
Evidence of common ancestors can be found in fossils and in living organisms.

10. Evidence of Ancestry, continued
Section 1 Change over Time
Evidence of Ancestry, continued
Drawing Connections Scientists examine the fossil record to figure out the relationships between extinct and living organisms.
Scientists draw models that show proposed relationships between ancient and modern organisms.

11. Section 1 Change over Time
Examining Organisms
Case Study: Origins of the Modern Whale Scientists think that the ancient ancestor of whales was probably a mammal that lived on land and could run on four legs.
Comparisons between modern whales and a large number of fossils have supported this hypothesis.

12. Evidence of Whale Origins: A
Section 1 Change over Time
Evidence of Whale Origins: A

13. Examining Organisms, continued
Section 1 Change over Time
Examining Organisms, continued
Walking Whales Each new species in the fossil record of the whale has shared traits with an earlier species.
Some species had new traits that were passed on to later species. In all cases, the organisms had traits that allowed them to survive in their unique environment.
Modern whales have hip bones, which is a link to their ancient walking ancestors.

14. Evidence of Whale Origins: B
Section 1 Change over Time
Evidence of Whale Origins: B

15. Section 1 Change over Time
Comparing Organisms
Comparing Skeletal Structures The structure and order of bones of a human arm are similar to those of the front limbs of a cat, a dolphin, and a bat.
These similarities suggest that cats, dolphins, bats, and humans had a common ancestor.

16. Section 1 Change over Time

17. Comparing Organisms, continued
Section 1 Change over Time
Comparing Organisms, continued
Comparing DNA Molecules Scientists also compare organisms at the molecular level.
Species that have more DNA in common are more closely related and have shared a common ancestor more recently.
The fact that all existing species have DNA supports the theory that all species share a common ancestor.

18. Section 2 How Do Population Changes Happen?
Bellringer
The following are traits that almost all humans have in common: upright walking, hair, fingerprints, binocular vision, and speech. List the advantages and disadvantages of each trait. Do you think the advantages are greater than the disadvantages? Why or why not?
Record your responses in your science journal.

19. Section 2 How Do Population Changes Happen?
Objectives
Describe how some finch species of the Galapagos Islands developed adaptations in response to their environment.
Describe the four parts of Charles Darwin’s process of natural selection.
Explain how variation in each species can occur.

20. Section 2 How Do Population Changes Happen?
Charles Darwin
In the 1800s, scientists were beginning to see evidence of change in the fossil record, but no one was able to explain how change happens until Charles Darwin.
Darwin signed-on for a five-year voyage around the world and worked as a naturalist.
His observations helped him form a theory about how change happens.

21. Charles Darwin, continued
Section 2 How Do Population Changes Happen?
Charles Darwin, continued
Darwin’s Excellent Adventure Darwin collected thousands of plant and animal samples. Observations made on the Galápagos Islands west of Ecuador were especially important to his theory.

22. Charles Darwin, continued
Section 2 How Do Population Changes Happen?
Charles Darwin, continued
Darwin’s Finches Darwin noticed that the finches of the Galápagos Islands were a lot like those in Ecuador. And the finches on each island differed from the finches on the other islands.

23. Section 2 How Do Population Changes Happen?
Darwin’s Thinking
Darwin hypothesized that the island finches descended from South American finches.
And Darwin suggested that over many generations, the finches developed adaptations for the various island environments.

24. Darwin’s Thinking, continued
Section 2 How Do Population Changes Happen?
Darwin’s Thinking, continued
Ideas About Breeding In Darwin’s time, farmers and breeders had produced many kinds of farm animals and plants. These plants and animals had traits that were desired by the farmers and breeders.
A trait is a form of a genetically determined characteristic.

25. Darwin’s Thinking, continued
Section 2 How Do Population Changes Happen?
Darwin’s Thinking, continued
The practice by which humans select plants or animals for breeding based on desired traits is selective breeding.
Most pets, such as dogs, have been bred for their desired traits.

26. Darwin’s Thinking, continued
Section 2 How Do Population Changes Happen?
Darwin’s Thinking, continued
Ideas About Population Darwin was influenced by an essay that described the reasons that human populations do not grow uncontrollably.
Darwin knew that the populations of all species are limited by starvation, disease, competition, and predation.
Darwin reasoned that the offspring of the survivors inherit traits that help the offspring survive in their environment.

27. Darwin’s Thinking, continued
Section 2 How Do Population Changes Happen?
Darwin’s Thinking, continued
Ideas About Earth’s History New ideas abut the age of the Earth provided enough time for adaptations to occur. This helped to support Darwin’s belief that species change over time.

28. Darwin’s Theory of Natural Selection
Section 2 How Do Population Changes Happen?
Darwin’s Theory of Natural Selection
In 1859, Darwin published a famous book called On the Origin of Species by Means of Natural Selection.
In his book, Darwin proposed the theory that change in populations happens through natural selection.
Natural selection is the process by which organisms that are better adapted to their environment survive and reproduce more successfully than less well adapted organisms do.

29. Section 2 How Do Population Changes Happen?
Copyright © by Holt, Rinehart and Winston. All rights reserved.

30. Darwin’s Theory of Natural Selection, continued
Section 2 How Do Population Changes Happen?
Darwin’s Theory of Natural Selection, continued
Genetics and Inherited Traits Today, scientists know that variation happens as a result of of the exchange of genetic information as it is passed from parent to offspring.
Some genes make an organism more likely to survive to reproduce.
The process called selection happens when only organisms that carry these genes can survive to reproduce.

31. Bellringer A mnemonic device is a trick that can help you
Section 3 Natural Selection in Action
Bellringer
A mnemonic device is a trick that can help you
remember words. Write down the four steps of
natural selection. Then create a mnemonic device to help you remember each step by using the first letter of the main word from each step as the first letter of a word in a phrase that is easy for you to remember.
Write your answer in your science journal.

32. Section 3 Natural Selection in Action
Objectives
Give two examples of how natural selection can result in an adaptation that helps an organism survive.
Outline the process of speciation.

33. Changes in Populations
Section 3 Natural Selection in Action
Changes in Populations
The theory of natural selection explains how a population changes in response to its environment.
Well-adapted individuals will likely survive and reproduce.

34. Changes in Populations, continued
Section 3 Natural Selection in Action
Changes in Populations, continued
Adaptation to Hunting Scientists think that hunting in Uganda is affecting Uganda’s elephant population.
Because ivory is very valuable, elephants are hunted for their tusks.
So, fewer tusked elephants survive to reproduce, and more tuskless elephants survive. Tuskless elephants pass the tuskless trait to their offspring.

35. Changes in Populations, continued
Section 3 Natural Selection in Action
Changes in Populations, continued
Insecticide Resistance Often, insect populations become resistant to insecticide because the insects produce many offspring and have a short generation time.
Generation time is the average time between one generation and the next.

36. Changes in Populations, continued
Section 3 Natural Selection in Action
Changes in Populations, continued

37. Changes in Populations, continued
Section 3 Natural Selection in Action
Changes in Populations, continued
Competition for Mates Survival of individuals does not guarantee survival of a species.
For organisms that reproduce sexually, competition for mates can select for adaptations.

38. Section 3 Natural Selection in Action
Forming a New Species
Sometimes, drastic changes that can form a new species takes place.
A new species may form after a group becomes separated from the original population.
The formation of a new species as a result of change over time is called speciation.

39. Forming a New Species, continued
Section 3 Natural Selection in Action
Forming a New Species, continued
Separation Speciation often begins when a part of a population becomes separated from the rest.
Adaptation Populations constantly undergo natural selection. After two groups have separated, natural selection continues to act on the groups.
If the environmental conditions for each group differ, the groups’ adaptations will differ.

40. The Development of Galápagos Finch Species
Section 3 Natural Selection in Action
The Development of Galápagos Finch Species

41. Forming a New Species, continued
Section 3 Natural Selection in Action
Forming a New Species, continued
Division Over many generations, two separated groups of a population may become very different through natural selection.
Even if a geological barrier is removed and the groups are reunited, they may no longer be able to interbreed.
If they cannot interbreed, the two groups are no longer the same species.

42. Section 3 Natural Selection in Action

43. Species Section 3 Natural Selection in Action
Click below to watch the Visual Concept.
Visual Concept

44. Population Changes
Concept Mapping
Use the terms below to complete the concept map on the next slide.
change DNA
evidence time
extinct species fossil record
living species body structures
common ancestors

45. Population Changes

46. Population Changes